The objectives of the proposed project will be to provide information regarding the maturation and function of the renin angiotensin mineralocorticoid systems in the sheep fetus and newborn lamb. This information may have relevance to development of fluid and electrolyte therapy schedules and blood pressure control for normal and sick preterm and term human infants. There are three main modulators of aldosterone secretion: ACTH, potassium, and the renin angiotensin system. The studies in the present grant will utilize the chronic fetal sheep preparation to study the maturation and function of the renin-angiotensin-aldosterone system in the fetus and in the newborn lamb. The studies will involve stimulation and inhibition of the renin-angiotensin-aldosterone system using furosemide, angiotensin blockers, changes in blood pressure, changes in potassium level and by assessing the response to salt loading. In addition, certain anatomic and functional maturation studies of the juxtaglomerular apparatus will be performed. The control of the renin-angiotensin-aldosterone system will be studied by using blocking agents for both adrengergic alpha and beta receptors and the effect of various modes of birth. The effects of the renin-angiotensin aldosterone system on glomerular filtration rate, tubular responsiveness, and sodium and potassium excretion will be assessed.